There is general agreement that a large number of peptides isolated from many different sources have specific effects on the nervous system where they can act as neurotransmitters or neuromodulators. Vasoactive peptides, hypothalamic releasing factors, gastrointestinal hormones, morphine-like factors and peptide hormones have been shown to exert a wide range of effects, from modifying the electrical activity of individual neurons to producing complex behavioral changes. We will initiate our studies on neuropeptides by isolating and characterizing the several peptide-like substances that we have found present in the central nervous system and that bind to the endorphin receptor. We will determine their molecular weight, enzyme sensitivities, and immunological characteristics as well as the nature of their interaction with the endorphin receptor. We will use enzymological and immunological techniques to search for pro-endorphins and for endorphin-converting enzymes. Immunological and radiochemical techniques will be used to determine the turnover rate of the different peptides that bind to the endorphin receptor. The isolation and characterization of neuropeptides will be one of the most fruitful chapters of neurochemistry in future years and will provide the basis for the study of their physiological and pathological significance.